Energy absorber and method of operating same

ABSTRACT

An energy absorber primarily intended for the arresting of aircraft, and a method of operating the same, said absorber having a chamber in which a liquid is pumped around a rotor and stator lattice structure having oppositely curved vanes and blades, with a portion of the liquid in a return chamber given a progressively increased tangential velocity in a potential vortex, and a remaining small portion of the liquid being passed to equal pressure channels to be combined at the rotor inlet, and the remaining portion of the liquid proceeding in a flow direction opposite to the direction of rotation of the rotor so that equal pressure flow compensates for the reduction in pressure of the vortex flow at the rotor inlet.

United States Patent [191 Carlsson et al.

[ 1 Jan. 9, 1973 [54] ENERGY ABSORBER AND METHOD OF OPERATING SAME [75]Inventors: Sixten Einar Carlsson; Lars Halvar Myhr; Lars-Ake ErllngSvensson, all

of Norrkoping, Sweden [73] Assignee: Borgs Fabricks Aktiebolag,Norrkoping, Sweden [22] Filed: Jan.8, 1971 v [21] Appl. No.: 104,963

[30] Foreign Application Priority Data Feb. 26, 1970 Sweden ..25l8/70[52] U.S. Cl. ..188/296 [51] Int. Cl. ..B64f 1/02 [58] Field of Search..l88/290, 296; 244/110 [5 6] References Cited UNITED STATES PATENTS3,599,906 8/1971 Reinemuth ..188/290 Primary Examiner-Edward A. SrokaAttorny-Munson & Fiddler [57] ABSTRACT An energy absorber primarilyintended for the arresting of aircraft, and a method of operating thesame, said absorber having a chamber in which a liquid is pumped arounda rotor and stator lattice structure having oppositely curved vanes andblades, with a portion of the liquid in a return chamber given aprogressively increased tangential velocity in a potential vortex, and aremaining small portion of the liquid being passed to equal pressurechannels to be combined at the rotor inlet, and the remaining portion ofthe liquid proceeding in a flow direction opposite to the direction ofrotation of the rotor so that equal pressure flow. compensates for thereduction in pressure of the vortex flow at the rotor inlet.

3 Claims, 3 Drawing Figures PATENTEDJAI 9197s WVBVIOR. Sixten EinarCarlsson, et a1 MUNSON & FIDDLER ATTORNEY ENERGY ABSORBER AND METHOD OFOPERATING SAME The present invention relates to an apparatus and methodof operating hydraulic energy absorbers, preferably absorbers used forarresting the movement of aircraft, and in which a liquid is pumpedaround a rotor and stator lattice structure, the blades of which arecurved in opposite directions.

Absorbers of this type are used as aircraft brakes and are soconstructed that the direction of flow of a liquid in a closed chamberis continuously changed by means of a rotor-stator lattice structure.With brakes of this description, the rotor imparts to the liquid aradial-tangential direction of movement. During the passage of theliquid from the rotor outlet to the rotor inlet, it is forced by astator lattice to move substantially tangentially to the inlet in adirection opposite to the direction of movement of the rotor lattice.

BACKGROUND OF THE INVENTION In the case of an energy absorber used foraircraft landing arrestors, the moment of inertia of the rotatingmembers must be as low as possible. In the majority of cases therotating members mainly consist of a band coiling device such as awinch, a rotor shaft, a rotor and the liquid present in the apparatus.

Since, for several reasons such as aircraft weight, speed andmaximum-permitted retardation, it is not possible to alter the moment ofinertia of the band-coiling device and rotor shaft to any appreciableextent, and it only remains to reduce the dimensions of the rotor.

The invention has reference to an apparatus and method for convertingenergy in such absorbers. The present invention provides a greaterbraking torque with a rotor of given dimensions than that obtained withsystems previously known. According to the apparatus and method of theinvention, the liquid flow is guided radially and tangentially to theinlet opening of the rotor in a direction opposite to the direction inwhich the rotor rotates, by means of a suitable vortex formed in theliquid. The so-called potential vortex is the most suitable form ofvortex for this purpose.

For a given speed of rotation and a given rotor it can be said thatwhere M is the torque of the rotor K is a constant v is the inletvelocity of the liquid in a tangential direction v: is the outletvelocity of the liquid in a tangential direction v, is contradirectionalto v;

This means that when the inlet velocity and the outlet velocity areequal and with the direction of flow of the liquid at the inlet beingopposed to the direction of rotation of the rotor, the torque obtainedis four times greater than that obtained when the velocity of theincoming liquid, tangentially to the rotor, is zero, that is, the flowof the liquid is purely radial.

The use of the potential vortex provides a considerable increase in thetangential velocity of the incoming liquid which, unless precautionarymeasures are taken, causes serious problems at the rotor inlet,occurring in the form of vapor formation and cavitation as a result ofthe low static pressure of the liquid. If the surface of the liquid isat atmospheric pressure, the low static pressure will cause a vortex tobe formed at the rotor inlet, thereby causing air to be drawn into therotor. This air causes stagnation of the flow of liquid and the torquefalls. The reduced liquid flow causes a reduction in the rate of flowand thereby an increase in the static pressure at the rotor inlet. Thevortex ceases with increased liquid flow and subsequently increasedtorque, and thereafter the cycle is repeated. The result is therefore apulsating torque, causing the efficiency of the device to be extremelylow.

The present invention rectifies thisphenomenon by conducting, from theregion of the liquid chamber at which a very high static pressureprevails namely, at the periphery, a small portion of the liquid andtransporting this liquid in channels of equal pressure to the inlet ofthe rotor, where a static pressure is applied to the vortex without anyappreciable reduction in the total tangential velocity of the liquid.

The result is a uniform and extremely high torque on the rotor shaft.One characteristic of liquid brakes of this kind is the lowbrakingtorque at low speed, this being shown by the equation M, k X wwhere M, is the torque k is a constant w is the angular velocity of therotor.

This characteristic is a disadvantage when the liquid brakes are usedfor aircraft landing arrestors, since the braking force becomes very lowat the end of the braking distance. This disadvantage is eliminated to acertain extent by using elastic line material which tends to maintainthe speed of the brakes at a high level when the load is relieved.

In order to further improve the low-speed characteristics of theapparatus and to enable less elastic line material to be used, theliquid brake of the present invention is supplemented with a hydraulicpump having a suitable torque and driven from the rotor shaft. This pumpdischarges into a hydraulic accumulator with a very flat characteristicand the pump torque will therefore be practically independent of thespeed of the rotor. The pump torque is adjusted to give a low butnevertheless appreciable addition to the braking torque at the end ofthe braking distance, without materially affecting the characteristic ofthe liquid brake apparatus.

DESCRIPTION The invention is illustrated in the accompanying drawing inwhich:

FIG. I shows a runway provided with aircraft landing barriers and anaircraft arrested thereby;

FIG. 2 is a view in vertical section of an absorber provided-with abrake drum, and

FIG. 3 is a horizontal view in section taken through the lines A-A, 8-8and C-C in FIG. 2.

In FIG. 1 an aircraft is shown at l, the same having been arrested by ahook mounted on it that has become engaged with a wire 2 connected to abrake band 3, which is unwound as the plane is brought to a stop, from aband drum 4 connected to a brake 5, one such brake being arranged oneither side of a runway 6.

FIG. 2 shows an absorber installed below the surface of the runway. Theabsorber consists of a liquid housing 7 in which is mounted a shaft 8that supports a band drum 4 at its upper end and at its lower end arotor 9 in the form of a blade ring. The rotor 9 is encircled by astationary guide vane ring 10, the vanes of which are curved in adirection opposite to that of the blades of the rotor. The blade latticestructure is located between the lower end wall 11 of the housing 7 anda ring 12 which is attached to the guide vanes on the ring and forms awall for the rotor passage. Located on the opposite side of the ring 12is a return chamber 13 for the liquid return flow to the rotor.

Along the upper end wall 14 of the housing 7 are arranged equal pressurechannels between the guide vanes 15 arranged between the end wall 14 anda wall 16, the guide vanes having channels of substantially constantcross-sectional area.

Connected to the lower end of the shaft 8 is a hydraulic pump 17, theinlet of which is provided with a' strainer 18 and the pump 17communicates with a liquid tank 19, the outlet of which is connected, bymeans of a pipe 20, to a liquid accumulator 21. At 22 is shown a valveby means of which the contents of the accumulator can be emptied intothe tank 19.

The absorber operates in the following manner:

When an aircraft is arrested by the barrier system, the band drum 4 willbegin to rotate, causing the rotor 9 to rotate and this induces theliquid to flow outwardly and substantially in a tangential direction.The flow of liquid is deflected in the guide vane ring 10 and leaves thering in a substantially tangential direction.

In order that a state of equalibrium may exist, the liquid is forced toflow radially toward the shaft in the return chamber 13 and into therotor as indicated by the arrows in FIG. 2. A potential vortex is formedin the chamber 13 between the ring 12 and the wall 16, hav-' ing atangential velocity component which increases a number of times towardthe rotor axis. The contradirectional flow gives a substantiallytangential inlet direction in the rotor lattice.

In order to raise the static pressure at the rotor inlet, a portion ofthe liquid in the chamber 13 is removed and is conveyed under constantpressure to the rotor inlet through the channels between the guide vanes15.

The aircraft is braked by the torque on the shaft 8 as a result of theliquid flow, and the energy is converted to heat in the liquid. Duringthe braking process, liquid in the tank 19 is forced into theaccumulator 21 by the pump 17, a torque on the shaft 8 relativelyindependent of the speed thus being added to the speed-dependent torquecaused by the liquid flow. When the aircraft has thus been brought to astop, the contents of the accumulator are emptied into the tank by meansof th valve 22.

What is claimed is:

1. A method of operating energy absorbers of the type in which liquid ispumped around a rotor and stator lattice structure having oppositelycurved vanes and blades and which is intended for arresting the movementof aircraft, characterized in that portion of liquid in a return chamberis given a progressively increased tangential velocity in a potentialvortex while a remaining smaller portion of the liquid is passed toequal pressure chambers to be combined in the rotor inlet with theremaining portion of the liquid in a flow direction which IS opposite tothe direction of movement of the i. a drive shaft mounted centrally insaid housing which supports a bladed rotor encircled by a stationaryguide vane ring member; I ii. a blade lattice structure'arranged betweenan end wall of said housing and a second ring member; Y a return chamberinsaid housing for the recirculation of the liquid to the rotor locatedat the opposite side of said ring member;

e. equal pressure channels in said housing through which a minor portionof the return liquid from the guide vane ring member is passed to therotor inlet;

f. said equal pressure channels being located along opposite walls ofsaid housing.

3. An energy absorber according to claim 4, characterized in that theabsorber is supplemented with a pump connected to the drive shaft and bymeans of which liquid is pumped from a tank to a pressure accumulator sothat a certain amount of energy is also absorbed at low rotor speeds.

1. A method of operating energy absorbers of the type in which liquid ispumped around a rotor and stator lattice structure having oppositelycurved vanes and blades and which is intended for arresting the movementof aircraft, characterized in that portion of liquid in a return chamberis given a progressively increased tangential velocity in a potentialvortex while a remaining smaller portion of the liquid is passed toequal pressure chambers to be combined in the rotor inlet with theremaining portion of the liquid in a flow direction which is opposite tothe direction of movement of the rotor, so that the equal pressure flowcompensates for the reduction in pressure of the vortex flow at therotor inlet.
 2. A rotary hydraulic energy absorber comprising: a. anannular housing for receiving liquid; b. a braking structure cooperatingwith the liquid in said housing to provide a retarding torque; c. saidbraking structure comprising: i. a drive shaft mounted centrally in saidhousing which supports a bladed rotor encircled by a stationary guidevane ring member; ii. a blade lattice structure arranged between an endwall of said housing and a second ring member; d. a return chamber insaid housing for the recirculation of the liquid to the rotor located atthe opposite side of said ring member; e. equal pressure channels insaid housing through which a minor portion of the return liquid from theguide vane ring member is passed to the rotor inlet; f. said equalpressure channels being located along opposite walls of said housing. 3.An Energy absorber according to claim 4, characterized in that theabsorber is supplemented with a pump connected to the drive shaft and bymeans of which liquid is pumped from a tank to a pressure accumulator sothat a certain amount of energy is also absorbed at low rotor speeds.